1. Field of the Invention
The present general inventive concept relates to an apparatus to and method of controlling a step motor, and more particularly, to an apparatus to and method of controlling a step motor by checking signals to control an operation of the step motor and resetting the apparatus controlling the step motor when signals indicating an abnormal operation, such as stepping out, of the step motor are detected, thereby preventing a fire or damage to parts caused by the abnormal operation of the step motor.
2. Description of the Related Art
A step motor rotates by a predetermined step angle in response to a pulse signal. The step motor has been widely used as a driving source for factory automation (FA) or office automation (OA) applications and, accordingly, the demand for a high-performance step motor has increased. In particular, the step motor is widely used as the driving source of inkjet printers, scanners, facsimiles, and laser printers that require highly precise position control and low noise level in various speed ranges.
The step motor may be settled by a combination of an excitation method and a driving method. The excitation method is classified into one-phase, two-phase, three-phase, and four-phase excitation methods according to the number of phases to which electric current flows at a time. The driving method is classified into a unipolar driving method in which electric current flows in a fixed direction and a bipolar driving method in which the electric current flows in a variable direction.
Hereinafter, the operation of the step motor will be described using the unipolar two-phase excitation method. FIG. 1 illustrates the operation of a conventional step motor using the unipolar two-phase excitation method.
Referring to FIG. 1, each of step motors 101, 102, 103, and 104 includes a stator and a rotor. When the stator is magnetized, the rotor including a magnet rotates around the magnetized stator. In other words, when the step motors 101, 102, 103, and 104 are to be driven in a clockwise (CW) direction, the stators thereof are excited in the sequence (A1, B1), (B1, A2), (A2, B2), and (B2, A1), respectively. Conversely, when the step motors 101, 102, 103, and 104 are to be driven in a counter clockwise (CCW) direction, the stators thereof are excited in the sequence (B1, A1), (A1, B2), (B2, A2), and (A2, B1), respectively.
FIG. 2 is a graph illustrating a linear acceleration/deceleration to prevent a conventional step motor from stepping out. Referring to FIG. 2, it is assumed that a step motor is used as a driving motor of a printer and rotates in the CW direction, thereby linearly driving a printer unit. In this case, the driving section of the step motor is divided into an accelerating section 200, a constant speed section 201, and a decelerating section 202. In the accelerating section 200, the step motor accelerates until it reaches a certain speed. In the constant speed section 201, the step motor moves at a constant speed. In the decelerating section 202, the step motor decelerates until it comes to a halt. When the step motor is driven in the CCW direction, its driving section is also divided into an accelerating section 204, a constant speed section 205, and a decelerating section 206. There is a suspension section 203 between the driving section of the CW direction and the driving section of the CCW direction. Reference symbol L indicates a distance traveled by a sheet of paper in the driving section of the CW direction.
In this conventional method of controlling a step motor, an acceleration/deceleration table (or an acceleration/deceleration lookup table) is used to enable the step motor to reach a desired speed. The acceleration/deceleration table is stored in a memory such as a read only memory (ROM) or a random access memory (RAM).
FIG. 3 is a block diagram of a conventional apparatus controlling a step motor. The apparatus includes a memory 420, a controller 410, a step motor driver 430, and the step motor 440. To control the step motor 440, the controller 410, which controls the step motor driver 430, generates an interrupt in the memory 420 whenever driving the step motor 440, reads an acceleration/deceleration table value, and controls the speed of the step motor 440.
Another conventional method of controlling a step motor in a stable manner by time adjustment is disclosed in U.S. Pat. No. 6,442,437.
Referring back to FIG. 2, to prevent the step motor from stepping out in the accelerating section 200, pulses are transmitted at irregular intervals. Generally, a step motor steps out when the driving torque is more than its pull-out torque. “Stepping out” refers to cases where the number of pulses transmitted to the step motor does not match the actual rotation of the step motor. To prevent this, in the accelerating section, pulse frequencies are set to a value smaller than target pulse frequencies as illustrated in FIG. 2.
Referring back to FIG. 3, in response to a step motor start signal, the controller 410 reads an acceleration/deceleration value stored in the memory 420, converts the acceleration/deceleration value into a predetermined step motor driving pulse, and transmits the step motor driving pulse to the step motor driver 430 such that the step motor 440 can be driven without stepping out.
When stopping the step motor 440, the controller 410 reads an acceleration/deceleration table value stored in the memory 420, converts the detected acceleration/deceleration table value into a predetermined step motor driving pulse, and transmits the step motor driving pulse to the step motor driver 430 such that the step motor 440 can be stopped without stepping out.
However, in this method of driving the step motor 440 according to the acceleration/deceleration table value, when the step motor 440 is driven abnormally, for example, when the step motor 440 steps out due to unexpected problems, the controller 410 fails to check the abnormal operation of the step motor 440, which may cause a fire or damage to motor parts due to an inflow of excess current.